MFH:- Prevent errors in CVS builds when bison is not there (for Sean :)

configure.in

@@ -151,6 +151,15 @@ PHP_PROG_AWK
 PHP_PROG_BISON
 PHP_PROG_LEX
 
+dnl Check if bison generated files exist when bison does not..
+case $php_cv_bison_version in
+  ""|invalid[)]
+    if ! test -f "$abs_srcdir/Zend/zend_language_parser.h" || ! test -f "$abs_srcdir/Zend/zend_language_parser.c" ; then
+      AC_MSG_ERROR([bison is required to build PHP/Zend when building a CVS checkout!])
+    fi
+    ;;
+esac
+
 dnl Platform-specific compile settings.
 dnl -------------------------------------------------------------------------